Electrooptical transmission system



Sept. 26, 1932. F. w. REYNQLDS ELEcTRooPTIcAL TRANSMISSION SYSTEMOriginal Filed Feb. 18, 1927 2 Sheets-Sheet l IN VEN TOR By F. w. REwvoL 05 A TTORNE V Lum .Sg-Qi.. E@ F. w. REYNQLDS ELECTROOPTIGALTRANSMISSION SYSTEM Original Filed Feb. 18, 192'? 2 Sheets-Sheet 2 .m@Fi /NVENTOR E W REYNOLDS ATTORNEY Patented Sept. 20, 1932 UNiTsD STATESlPATENT .LoFi-ics FREDERICK W. REYNOLDS, OF GIR-ANTWOOD, NEW JERSEY,ASSIGNOR TO AMERICAN TELEPHONE AND' TELEGRAPH COMPANY, A CORPORATION OFNEW YORK ELECTROOPTIGL TRANSMISSION 'SYSTEM :Original application ledFebruary 18, 1927, Serial No. 169,322. Patent 1,773,119, dated August19, 1930.

Divided and this application led July 17, 1930. Serial No. 468,702.

` rfhis invention relates .to electro-optical` paratus may be used foreither transmission or reception, and hence the invention serves tosimplify the terminal equipment which is used for the transmission ofpictures over telephone circuits. j

In an embodiment of the invention selected for illustration a string orribbon electro-` mechanical light valve such as disclosed'in Patent No.1,667,805, May 1, 1928, of Herbert E. Ives, is positioned between asource of light and a holder 'for the transmitting or receiving film,depending upon whether transmission or reception is taking place. Forpicture transmission the light valve ribbon is vibrated by alternatingcurrent from a vacuum tube oscillator or other suitable source at asubstantially constant frequency thereby generating a pulsatinglightbeam which is hereinafter called a carrier light beam. This carrierlight beam is modulated by the picture at the transmitter and issubsequently directed onto a photoelectric cell which in turn producespulsating photoelectric currents representative of the light effects ofthe picture. By means of a transformer, these currents set upalternating current which constitutes the modulated carrier current forthe line. For reception at the same terminal station, the oscillator isdisconnected from the light valve and the incoming carrier picturecurrents are impressed upon this valve thereby4 causing to pass to thefilm holder, which now holds the receiving film, a'varying beam of lightcorrespondingtothe light intensities of the elemental areas ofthepicture which is being transmitted from the distant station. Thescanning at the terminals may be carried on in accordance with standardpractice Well known in the art. A suitable 'scanning systemis'dis'closed in Patent No. 1,7 06,032, March 19,1929 ofv M.V B.

lar parts of the apparatus.

Long. The level of the line carrier currents i may be raised at thetransmitting terminal,

kto minimize the eiect of disturbances enternecting stations showingterminal -apparatus which may embody this invention. p

Fig. 2 is a detail, showing the lightvalve ribbon with relation to thelight valveapertures when no current is flowing.

Fig. 3 is a curve, showing the variation in the intensity of theillumination of the picture at the transmitter with time. y

Fig. l is a curve,showing`-the'photoelectric current resulting fromlight modulation by the varying picture density plotted against time.

Fig. 5 is a general schematic arrangement of the terminal apparatus ofone station, showing an embodimentV of the invention comprisingapparatus which may replace certain parts of the apparatus of Fig; y

Similar reference characters refer to simi- In Fig. 1, in which twointerconnected stations are shown'7 the terminal at the left,-designated station W, will be described asy a transmitting station andthe switch at this station is :accordingly kthrown to the right; whilethe terminal at theright, designated station E, will be considered as areceiving station and the switch'lO of that station is also thrown tothe right, thus connecting theterminal apparatus of kthe two Vstationsfor transmission Vand receptiomrespectively. y 4

VAt station W, light valve is positioned in the path of light obtainedfrom Vany suitable source 21. f A suitable lens system 22, 23 and 24land aperturedV members 25 'and 26 cause a beam of lightV to'passthrough-l the 'sticefinpicture transmissionssystemsftherebycausingtire light beam -to successively scan the elemental areas of theentire picture.

It is preferable to mount-thelightvalve and thepicture holdingldrum sothat the axis 'of' the light'valve ribbon andfthe drum are at rightangles toea'ch'other.

The li ht beam, after passing through the l .picturqis .reflected 90 byaprism ormirror G01-:mdpassedthroughV aliens system 61- to the lightsensitive cell lY0. "The -lightsensitive cell, .upon 'being' activatedby the: varying light, causes varying electric" currents to be.transmitted .to the "amplifier 80. The amplifier connects throughthesWitchSlto the cir- :cuit 82tvhich intur-nconnects throughbladesTheoutgoing circuit 90 connects-through the filter 91 and the terminal.amplifier 92 lwith. the transmission linefleading V,to a receivingstation.

- 'QT-he .lightbeam activating'the .light sensitive cell 470v-is..a..pu'lsati.ng or carrier light .beam-andthe variationlzin theintensity of the/.beam isca'used by the light valve :20.

The ribbomofstheilight valve 20 is energized vbycan oscillator-'30 whichgenerates a sinusoi dal lWave ofthe order Vof1000 to 2000 or more cyclesper'second. -The voscillator 30 transmits its currents through blades13- tand ,-1.4 of-fswitcl1l0-=and .a connecting .circuit Vto.the-amplilierliO Where the o'scillatingV current is amplified and theoutput current of .the iamplifienpassed through `the .ribbon 27 ofthe'.'valve thereby causing thezlightvalve '.-ribbonto oscillate .atla.substantially constant Afrequency.4 `liovernent of Athe light valveribbon thus causesthelight lbeam-to rapidly vary .in `intensity in.accordance .with the frequency ofthe output current of the oscillator.Thebiasingbatteryl .and the high resi-stan ce 4.2 'afford:meansrtor adjustmgl the relation of fthe light valveirbbon respect A tof .tli1efl-ight valvefaperture.

. r-Ithas-.beenfound desirable 'iintheftransmission pictures .to zprOYde; for: festablishing` aldetinite rratio. between the maximum aandminimum picture currents transmitted, and to :provide for thetransmission -olf V`a 'definite minimum carrier-current .at all timesYeven-.When no light.` reaches the `light sensitive cell. The purpose ofthis is to avoid-overloading fthe 'transmission circuit.- apparatussuchasfrepeatersfand also to avoid inducing "cross-talk :in :neighboringcircuits, and .to yinsure 1 that the rlpi'cture -fcurrents transmitted iwill be fat inne-energy sufficienti to2 Iavoid 4serious interferencefrom noise currents. This may be accomplished as shown in Fig. 1 byusing a part of the output current of the oscillator and adding it tothe amplified picture currents, provision being made for adjusting.both'theg phase andthe magnitude of the former current With respect tothe latter or vice versa.' 4One Way of adding a part of Lt'hefoscillatoroutput .to the picture current tis Iicy: means of Lthe phase adjuster 85and associated potentiometer 86, Which connect the'output"s'ide--oftheamplifier 40 through the circuit comprisingrthe blades 15 and 16 yoftheswitch'l'O andthe switch 87 to 'the circuit 82; I By means-of the phaseadjuster Which may comprise Ma suitable network of variable im-.pedances arranged in accordance with principles Wellknownto theAart,.a:nd the assofciated potentiometenthe outputfcurrent of theoscillator canbephased With the picture current,..and the necessaryunmodulated carrier current of the proper amplitude im- .pressed upon`thetransmission circuit. y With such- .adjustment .the "shunted carrierandthe vvariable picture currents add directly. The variations in lightshades or tones of the. pic- .ture varerepresented in this case by acurrent in the output circuit of the lightsensiti-vefcell-70,Who'selfrequencyis the .frequency vof--th'e currentimpressed uponthe light valve ribbon and --Whose amplitude fatanyinstant Vis proportional to the light transmittedfby ntheypicture. t

If theflightvalveis adjustedso that When .there is no current flowingthrough its ribbon,'thezribbonguncovers one-half of the flight 1val-ve,aperture, then the illumination -will have :1a-sinusoidal formrepresented by sa. constantadded Vto a sine function, and at .the same'frequency las the-current impressed `upon-"the light valve ribbon, butWith a phase displacement-between its sine Vform com-pof nent and y thecarrier -of approximately 180 4orlm-ultiple.thereof. The width of thelight -valveribbonfshould-be equal to that of the lightvalvefaperturefand' its maximum ampli- VVtude ofv vibrationfshould beWithin one-half itsl'vvidth.

It Vis obvious-that vthe amplified photoelectric current VWilladddirectly to vthe 1 shunted output current ofthe oscillator 'if the.phase Vofthe latter current is adjusted -relati-'vely'ztot'he former.The phase adjust- VV`-er185 '-isfadapted to bring -about the necessaryphasev adjustment. This/arrangement of the -lfightzvalvein associationwith the light sen- ;sitive cel'l'fis such that the varying currents-fromfthe'icell -have'the-'same frequency as the variations of 'theflighttransmitted by the light valve andalso the same frequency asl :thecurrent .from the oscillator operating the light' valve.. 'Thisarrangement is important forY if'fthe-.light :valve ribbon Weredifferently .adjusted respect to the light valveaperlli ture with nocurrent flowing through the rib-A bon, a double, frequency in the lightsensiwould make it more difficult to add` the de- Y sired carrier to thepicture current.

In adjusting the apparatus for transmitting a picture it may beadvantageous toascertain the amount of current transmitted by thebrightest and by the darkest portions of the picture and f'ordetermining this a. measuring device 83 is arrangedso that by thro-wingswitch 81 to its upper closed position the output circuit of theamplifier 8() may be connected to this measuring device. Upon placing inthe light beam various portions of the fihn 50, or any other object ofvarying transparency, its transparency at different spots may bemeasured and indicated by the measuring device 83 in such units as maybe desired. For example, the measuring device may have a scalecalibrated to read in per cent of the total light. `When putting theapparatus in operation, the operator having ascertained the transparencyof the lightest and the darkest portions of the picture may use thisinformation in adjusting the apparatus for transmission.

The same measuring device 83, which may comprise a suitably arrangedvacuum tube amplifier-detector unit, is also used for indicating whenthe phase difference between the photoelectric current and the shuntedoscillator output current is zero. In making such a comparison, both theswitches 81 and 87 are thrown into their upper closed position, therebycausing the out-put from both the light sensitive cell 70 and the phaseadjuster 85 to be impressed simultaneously upon the measuring device 83.Also the ratio between the maximum and minimum picture currents, and themagnitude of the shunted oscillator output can be determined by the useof this measuring device 83 and proper manipulation of the switches 81and 87 for connecting it to the two circuits. The magnitude of thepicture current can be adjusted in a number of ways wellfknown to theart, such as, by varying the voltage impressed upon the light sensitivecell.

The descriptionso far has related primarilyv tothe apparatus arrangedfor transmitting. When arranged for reception, a part of the sameapparatus as is `employed for transmission is used, and its connectionisshown in the terminalstation E at the right of Fig. 1. -The switch 11()is thrown right and the relation of the light valve ribbon 127 withrespect to the light valve aperture arranged so that with no currentflowing through the ribbon the light valve is closed.-

VlVhen the switch 110 is thrown to the right blades 111 and'112 areoperative to connect the circuit 190 with the amplifier 140 and thelight valve ribbon 127. Theother four blades 113, 114, 115 and 116 areinoperative to the and hence the oscillator 130 and the phase ad juster185 are. disconnected from the oper ,ating circuit.

. The-proper relationship of the light valve ribbon to the light valveaperture may be established mechanically by adjustingV the light valvejaws or electrically by means of the biasing battery 141 and thepotentiometer 142. The incoming picture current is ampli- `hed by theterminal amplifier 192 and then passed through the filter 191, theamplifier 140 and the light valve ribbon to control its movement in amanner to reproduce the light effects of the distant picture and cause alight beam to be impressed upon the photo-sensitive film 150 on thecylinder 151, which is mov-ed in synchronism and in phase with thepicture at the transmitting stat-ion in accordance with standardpractice-well known in the art. Light from a steady source 121' pbe'required are employed for reception as are used for transmission andthe principal adjustment necessary to put the terminal equipment intoproper relationship for transmission or for reception are the circuitchanges governed by the switches 10 and 110 at the terminals and theproper adjustments of the light valve ribbon with respectto the'lightvalve aperture when no current is fiowing. The interchangeability ordual use of the apparatus units for either transmission or receptionsimplifies the terminal equipment and its operation.

The relation of the light valve ribbon to the light valve aperture whenno current is flowing is such that for transmission the light valve ishalf open and for reception the light valve is substantially closed asis shown at T and R, respectively, in Fig, 2. The primary reason'for thehalf open position when no current is flowing whe-ntransmitting, as

already explained, is to produce a varying illumination which whenimpressed on a light sensitive cell causes the latterV to set up avarying photoelectric current of the same freis necessitated by the factthat the photoelectric current approaches zero when a dark Y portion ofthe picture isbeing transmitted and a maximum when the lightest portonof the picture is being transmitte Adjustment of the relationshipbetweenV the `light .valve ribbon and the light valve aperture, yasdescribed in connection with Fig.

1, is effected by passing the properbiasing current through the lightvalve ribbon to cause to takel up the proper Yposition `'forv"transmission .or for reception. This requires adjusting the biasingcurrent When the'light valve is Vchanged from transmitting to receivingor vice versa. f

I-nFig. 2 isshoWn a mechanical means for making this-change. Tivo lightvalve Vapertures Tand'R are used and permanently pofio . arrangementsuch as the opaque shutter 29r sitioned inthe apertured member 28 inproper relationship tothe light valve ribbon. Only one of theseapert-ures isopen at a'time. This .may be mechanically eected vby anysuitable capable of being positionedzini front. of either v adjusted, isapproximately alinear-function of the current input to the lightvalveribbon so that the distortion from this source ,is negligible. v'Thispulsating illumination has been described herein'as producinga carrierlight vvbeam' andl as already explainedit is impressed by means of asuitable'optical .system upon elementalareas of the picture `Whose imageis "lio being transmitted. One reason for employing a pulsating carrierlight beam is to make possible the kuse of an alternating currentamplilier, and thus Vuse a `.pliotoelectric` current under conditionsWhich permit of its being ampliedwith ordinary voicefrequencyalternating current vacuum tube amplifiers. 'Iheemployment of suchapparatuspermits its use on existing telephone crothertrans- 'missioncircuits.

The pulsating carrier light beam in passing through the picture at thetransmitter is modulated in accordance Withthe light density of theelemental areas of thepicture and the cur- 4rent Yvariations resultingfrom` the modulated light beam being impressed upon, the photosensitivecell at the transmitting station may be representedby a curve havingasubstantially uniforml fundamental frequency'but of .varying amplitudeas shown in Fig. 4. :The .fundamental frequency ofthe photoelectriccurrent as heretofore explained is the same as that of the illumination.

g The unmodulated Vcarrier current which is impressed upon thetransmission circuit at -all times, irrespective of the photoelectriccurrent, may be obtained as vdescribed in Fig.

'l by shunting a part of the oscillator output current to .the outgoingcircuit.

In accordance With this invention. an optical arrangement 'for supplyingthe modulatedV carrier is shown in Fig. 5. In vthis ar-` rangement, apart of the. carrierv light beam is diverted'byvvmeans ofapartiallytranspar- Sent mirror 210, positioned in? the'path'of the light beam, insuch relation that it diverte a small percentage ofy the totalrlightjto'tlie light sensitive cell`70. `In the path ofthe light divertedto the -light l.sensitive cell, is

afplane or preferably' a concave mirror 211 and an adjustable aperture212 arrangedv for directing and controlling the diverted light.

By such any optical arrangement the major portion f the carrier lightbeam passes through the mirror l210 to the picture, and a minor portionof the light is diverted tothe light sensitive cell which is therebyactuated t0 produce unmodulated current of carrier.y

frequency. Whenv the .apparatusis used Vfor receiving, thesemi-transparent mirror 210 is moved out of the path of the light beaminto the v position` indicated at 213. 'The current produced inthe lightsensitive cell vby the tivo parts of the light beam ivill be insynchronisin andy in-pliase and.y consequently add directly to eachother. Themagnitude of the carrier `current'prod-uced bythe deflectedvpart of the light beam may be adjusted vby means of the-` aperture 212.

`'Iheterminal apparatus shown in Fig. 5 with the exception oft-lie`omission of the electrical sliunt'and the substitution-r.ofv the opticalshunt, above described for impressingV carriercurrent on the outgoingcircuit, is the sameas Fig. 1, and with the exception ofthese Idifferences, the same description applies to both figures.

lVhat is claimed is:

1. In an electro-opticall system, a source of*y steady light, meanstointermittentlyvary a beam'from said source, means to further vary saidbeam in accordance with signals, means toproduceza signal modulatedcarrier cur.

rent from said beam, and means dependent upon the operation of saidintermitten beam varying means to control the amplitude of the componentof carrier frequency in said modulated carrier current. v

V2. In Aan electro-optical transmissionV sys-H tem, a transmissioncircuit, alight beam, ia light interrupterrapidly and regularlyinterrupting saidbeai'n at a substantially uniform frequency therebyproducing carrier f pulsations, a light modulating picture fpositionedin the of the said light beam,l alight sensitive element excited by-the'said Ylight beam subsequent ato the said picture iio modulating thesaid lightbeam, and .anoptiv cal shunt passingpulsating light aroundfthesaid light modulating picture for `applying -uninodulated carrier lightpulsations producedv .by said light interrupter to the said lightsensitive element." l

3. An electro-optical system comprising a sourcer of steadyy light,meansV for cyclically varying a light'beamsupplied by said' source andfor producing an auxiliary light beam therefrom,'means for varying saidVfirst menl tioned beam in accordance-With signals, "and l means uponwhich said signal varied and auxiliary beams are incident to producesignal modulated carrier current. A

4. An electro-optical system comprisinga source of steady light, meansfor cyclically varying a light beam supplied by said source, means fordiverting light radiations from said beam to produce an auxiliary beam,means for varying said first mentioned beam in accordance with signals,and means upon which said signal varied and auxiliary beams are incidentto produce signal modulated carrier current.

5. In an electro-optical transmission system, a transmission circuit, ananalyzing light beam, a light interrupter in the pathof said light beam,means for controlling the said light beam to produce a modulated carriercurrent in said circuit, and means acted upon by said analyzing beam toproduce a second light beam for controlling the production ofunmodulated carrier currentto establish a minimum transmission level insaid circuit.

6. In an electro-optical transmission system, a transmission circuit, ananalyzing light beam, a light interrupter in the path of said lightbeam, a picture whose image is to be transmitted, means for controllingthe said light beam to produce a modulated carrier current in saidcircuit varying according to the lights and shades of the said picture,and means acted upon by said analyzing beam to produce a. second lightbeam for controlling the establishment of a definite ratio between themaximum and minimum current representing the darkest and lightest areasof said picture.

7 The method of carrier current signaling which comprises producing twobeams of light from a single source of light which is modulated atcarrier frequency, impressing a signal upon one only of said beams, andsimultaneously utilizing said beams to set up a carrier currentmodulated in accordance with said signal.

8. A signaling system comprising a source of uniformly periodicallyvarying light, means for modulating light in accordance with signals,means for directing light from said light source to said last mentionedmeans, light sensitive electric means receiving signal modulated lightfrom said modulating means, and means for simultaneously impressing uponsaid last mentioned means light from said source which is not modulatedin accordance with signals.

9. A signaling system comprising means for producing two uniformlyperiodically varying separate beams of light, the variations of saidbeams being in phase with each other, means for modulating one only ofsaid beams in accordance with signals, and light sensitive electricmeans simultaneously receiving said signal modulated beam and said beamwhich is not signal modulated.

10. In an electro-optical system, means to produce a. uniformlyperiodically varying beam of light, means to vary said beam inaccordance with signals, means to produce a signal modulated carriercurrent from said beam, and means to control the amplitude of thecomponent of carrier frequency in said modulated carriercurrentcomprising light sensitive electric means and means forimpressing thereupon a second beam of light having uniform periodicvariations similar to and in phase with thoserof the first beam.

In testimony whereof, I have signed my name to this specification this16th day of July 1930.

FREDERICK W. REYNOLDS.

